<a href="javascript:;" ng-tap="voltar()">Voltar</a>

<form>
    <label>Adicionar:</label>
    <input type="text" ng-model="obra.nome" />
    <button ng-click="inserir(id, obra.nome)">Adicionar</button>
    <a ng-tap="listarObras()" href="javascript:;">Obras</a>
</form>